A magnetic head and disk tester is an instrument that is used for testing the characteristics of magnetic heads and disks, such as a signal-to-noise ratio, track profile, etc. The tester should simulate those motions of the head with respect to the disk and the same rotational speeds of the disks that occur in an actual hard disk drive during operation. Each tester consists of two components, i.e., a mechanical component, commonly referred to as a spinstand, that performs movements of the head with respect to the disk, and an electronic component that is responsible for measurement, calculation, and analysis of the measured signal. The spinstand is also a mechanical component of a servo-writer, an instrument that is used for writing servo information on a magnetic disk, as well as a component of a flying height tester; an instrument used for measuring the flying height of a head over the disk.
An example of a prior art spinstand for a head and disk tester is illustrated in FIG. 1 (front view) and FIG. 1 (top view). The spinstand includes a stationary base plate 110 that supports walls 112a, 112b, 112c. The walls 112a, 112b, 112c in turn support a spindle 113 for carrying a disk pack DP disposed in a cylindrical disk pack region including one or more magnetic disks 114, having diameter D, and being coaxial about a disk pack axis DPA. The spindle 113 and the disks 114 are rotated by a spindle motor 115 about a spin axis SA.
The base plate 110 further supports first and second slide motors (not shown). The first slide motor moves a slide 116 along rails 117a, 117b in the Y direction (see FIG. 12). Two additional rails, 118a, 118b, are mounted on top of slide 116. The second slide motor controls movement of a second slide 19 along rails 118a, 118b in the X direction. The first and second motors cooperate to position a rotary positioner 120 mounted on slide 119 to a specified location with respect to the center of spindle 113. Rotary positioner 120 carries and positions magnetic head(s) 122 relative to disk(s) 114.
Another example of prior art spinstands for a head and disk tester include the Guzik V2002 XY-positioning spinstand and the Guzik S-1701B Micro Positioning Spinstand, both of which are available from the assignee of the present disclosure, Guzik Technical Enterprises, 2443 Wyandotte Street, Mountain View, Calif. 94043, USA (www.guzik.com).
As the density of magnetic recording increases, additional information tracks are compressed into a given disk area. The decrease in track size heightens the demand for improved accuracy in head positioning. Likewise, the rotational speeds of the magnetic disks increase in order to achieve shorter access times. In addition, more disks are added to the disk stack to provide additional storage.
As the disk(s) rotate, vibrations in both the disks and the magnetic heads may be induced. These vibrations increase track misregistration. In some cases, track misregistration reaches unacceptable levels at which spinstand operation becomes unreliable.
As described in U.S. Pat. No. 4,958,839, a prior art solution to this problem by Guzik Technical Enterprises is a ball-type clamping mechanism for clamping computer hard disks in a disk tester for accurate measuring of the disk's parameters comprises a cup-shaped support which is installed on a rotating part of the tester and serves to support a computer hard disk which rests on the upper surface of the support. The support has a cylindrical opening with a diameter equal to or slightly greater than the diameter of the disk opening. Slidingly inserted into the support is a cylindrical retainer which carries clamping balls uniformly spaced from each other in a circumferential direction and located in recesses formed in the side wall of the retainer. The balls have a diameter larger than the side wall of the retainer. A pull rod passes through the central opening in the bottom wall of the support and carries a clamping cone which is made from a resilient material softer than the material of the balls. When the rod is pulled down, a conical surface of the clamping cone pushes the balls radially outwardly into contact with the inner periphery of the hard disk, so that the disk is clamped. The number of balls exceeds three, so that a uniform clamping force is provided on each of the balls. Because the cone is made from a resilient material, the balls clamp the disk with a uniform force without the necessity of manufacturing the parts with accurate tolerances. This method allows quick replacement of a disk, but it can still distort the disk due to the discreet number of clamping points. Furthermore, the overall clamping force is limited, potentially resulting in instability.
A more common prior art solution, that securely holds the disk with adequate force, is a chuck consisting of a cap assembly and a base assembly. The cap and base assemblies clamp the disk to the spindle by use of a screw that passes through the cap and threads into the base. The screw attaches the cap to the base, clamping the disk with a force proportional to the fastening torque of the screw. This method is superior for head testing, headstack testing, and any other use that does not require frequent changing of the disk. However, this method creates problems for testing where the disk must be replaced repeatedly. The force is dependant upon the fastening torque, which can vary from one assembly to another, and the screw must be manually inserted and removed with each disk change, adding significant time to the process. Using a screw to hold the cap against the disk also makes automation of chuck insertion and removal difficult.
What is still desired is a new and improved apparatus and method for securing disks on a spindle of a spinstand. Among other aspects and advantages, the new and improved apparatus and method of the invention reduces vibration and track misregistration while decreasing overall testing times by clamping the disk without a mechanical fastener, decreasing operating times and allowing for the possibility of disk clamping automation. In addition, the new and improved apparatus and method preferably consistently and quickly secures a disk to a spindle of a spinstand with a known and repeatable clamping force, without adding additional unbalance to the system.